New hydrogenation catalyst for elastomers, and the process of hydrogenation

ABSTRACT

The invention relates to the hydrogenation of an unsaturated elastomer in the presence of a catalyst which is the coordinating complex of cobaltous chloride and 1 to 8 molecules of lactam or another amide or urea reduced by a trialkyl or triaryl aluminum or a dialkyl or diaryl aluminum hydride.

United States Patent [191 Halasa Mar. 18, 1975 NEW HYDROGENATION CATALYST FOR ELASTOMERS, AND THE PROCESS OF HYDROGENATION [75] Inventor: Adel Farhan Halasa, Bath, Ohio [73] Assignee: The Firestone Tire & Rubber Company, Akron, Ohio [22] Filed: Dec. 13, 1973 [21] App]. No.: 424,264

[52] US. Cl 260/94.7 H, 260/82.l, 260/83.3, 260/85.1, 260/85.3, 260/96 HY [51] Int. Cl C08d 5/00 [58] Field of Search 260/94.7 H, 96 HY, 82.1, 260/85.1, 85.3

[56] References Cited UNITED STATES PATENTS 3,412,174 11/1968 Knoll 260/683.9 3,531,445- 10/1970 Yoshimoto et a1. 3,673,281 6/1972 Bronstert et al. 260/94.7 H X Primary Examiner-William F. Hamrock [57] ABSTRACT 3 Claims, N0 Drawings NEW HYDROGENATION CATALYST FOR ELASTOMERS, AND THE PROCESS OF HYDROGENATION The invention relates to the catalytic hydrogenation of unsaturated elastomers. It includes the new catalyst which is employed.

The elastomer may be a natural rubber or a synthetic rubber. as for instance, polybutadiene, polypenteneamer or polyisoprene; an alternating copolymer of butadiene-ethylene, butadiene-propylene or butadieneacrylonitrile; butadiene-isoprene; ethylene-propylene terpolymer (EPT); or a copolymer of butadiene'or isoprene with l styrene or an alkyl derivative of styrene (e.g., alpha-methyl styrene, etc.) or (2) acrylonitrile. The hydrogenation of such elastomers is known in the art.

The catalyst is a coordination complex of cobaltous chloride with a lactam or other amide or urea in which the cobaltous chloride is present in the complex to form either an inner or outer complex. The reduced reaction product, a cobaltous chloride.(caprolactam) 8 coordination complex, is the preferred hydrogenation catalyst.

Various advantages are found in the use of the catalyst of this invention. It is soluble in hydrocarbon solvents. Because it forms a homogeneous solution, it is easily handled and can be used in continuous hydrogenation processes.

The hydrogenated elastomers. depending on the degree of saturation, are useful as thermoplastic elastomers. They are stable at high temperatures and are resistant to oxidative degradation. They are useful for the manufacture of tires, shoe soles, hoses, luggage, upholstery in automobiles, etc., and are useful as adhesives.

Kroll U.S. Pat. No. 3,412,174 uses the reaction product of a transition-metal salt (e.g., a cobalt salt ofa carboxylic acid), an organometallic (e.g., triisobutyl aluminum) and a Lewis base, as a catalyst for hydrogenation. The catalyst is ineffective at high temperatures and unstable over a long period of time. The patent does not suggest the use of lactam in producing the catalyst reaction product, nor does it suggest the use, alternatively, of an amide or urea as contemplated herein or the use of the reactants in the preferred ratio disclosed herein.

The cobaltous chloride coordination complex with caprolactam, etc. is readily produced by gently heating a solution of the lactam or other amide or urea with cobaltous chloride to form the coordinating complex and then reacting this cobaltous chloride complex in solution with the aluminum reducing agent.

The following are illustrative of the lactams, other amides and ureas that may be used.

The following are illustrative of the lactams, other amides and ureas that may be used.

The general formula for the lactams is in which n is 0 to 20. Caprolactam in which n =4 is preferred.

The general formula of the other amides is:

Aeetamide L 3 0 Acid amide g HzN- CH;

O N -methylaeid amide I g CHr-N- CH O N-methylbenzamide p;

Ureas may-fi-ry-n, in which R1, R2,

R2 Rs 7 R and R are the same or different and each may be hydrogen, a straight or branched chain (saturated or unsaturated) or cyclic alkyl group of I to 8 carbon atomsor an aryl group from the class consisting of phenyl, tolyl, xylyl, etc. The following are illustrative: urea, methyl urea, dimethyl urea, ethylhexyl urea, dioctyl urea, diallyl urea, diphenyl urea, butylphenyl urea, etc.

The reaction is preferably carried out in toluene, but other solvent (usually aromatic) in which the reaction product is soluble may be used. The reaction product is isolated and characterized.

The cobaltous chloride.hexaor octa-lactam or other complex is then reduced with a trialkyl or triaryl aluminum or a dialkyl or diaryl aluminum hydride. The alkyl groups may comprise 1 to 8 or more carbon atoms and the aryl groups comprise phenyl, tolyl, xylyl, etc. Mixed alkyl and aryl groups may be present as in dialkyl phenyl aluminum, etc. Trimethyl or triethyl or triisobutyl aluminum or diisobutyl aluminum hydride is preferred. During the reaction of the cobaltous chloride lactam complex or other complex with the aluminum reducing agent, a reduced product is formed which is active in hydrogenation of unsaturated polymers and may have other uses.

The preferred molar ratio of the cobalt chloride to the lactam, etc. to the aluminum compound is 1:616 or 1:828. However, more reducing agent can be used, but is unnecessary and uneconomical. The presence of the lactam or the like in the hydrogenation catalyst medium stabilizes the intermediate Cobalt which is the active catalyst in the hydrogenation and makes the hydrogenating compound soluble in the reaction medium and prevents it from aggregating into an insoluble compound.

The molar ratio of the reducing agent to the transition metal complex of the lactam, amide or urea is very critical. At Al/Co ratio of 10 or more, a disadvantageous increase in the molecular weight of the polymer is produced. Sometimes the reaction leads to gelation.

The prefcrred ratios of Al/Co are 611 and 8:1.

The molar ratio of the transition metal to the lactam, amide or urea in the reaction is very critical. The best ratio is 6 or 8 lactams, amides or ureas/l cobalt salt, such as the chloride, bromide or iodide.

Cobaltous chloride.(lactam, other amide and urea) a are not known in the literature. None of the cobalt chloride complexes are known in the literature. They have a definite structure. The complex may be an outer or inner complex. The geometry of the preferred lactam complexes may be suggested by the following structures:

Lactam Lactarn Lactam Outer Complex Inner Complex but there is no certainty that these are the actual formulae. In any case, both compounds, after reduction by trialkyl or triaryl aluminum or dialkyl or diaryl aluminum halide, can be very satisfactorily employed as active catalysts in the hydrogenation of elastomers.

It should be understood that cobaltous chloride forms a soluble complex in a hydrocarbon solvent with a variety of organic compounds such as lactams, amides, ureas, or other compounds having nitrogen adjacent to a ketone or aldehyde group. These complexes are all useful as hydrogenating catalysts when reduced with trialkyl or triaryl aluminum or with dialkyl or diaryl aluminum hydride. Complexes of cobaltous chloride with bicaprolactam, tricaprolactam and tetracaprolactam have been made and tested as hydrogenation catalysts. The inconstant hydrogenation rate and activities of the complexes makes them undesirable. However, only the cobaltous chloride.hexacaprolactam and cobaltous chloride.octacaprolactam have been found to be satisfactorily active at high temperatures in the range of 200350 F. and gave duplicable results and worked continuously. The other complexes of cobaltous chloride with caprolactam worked but are not preferred in this process.

The following which refers to the preparation of cobaltous chloride.(lactam 3 illustrates, in general, the preparation of any cobaltous chlorideamides or cobaltous chloride.urea. The use of the catalysts which follow illustrate the hydrogenation of unsaturated elastomers.

PREPARATION OF CATALYST This refers to the preparation ofcatalyst from caprolactam, but is illustrative of the general procedure for producing catalysts from other lactams, other amides, and ureas.

In preparing the catalyst from caprolactam, 18.0 mM of caprolactam (anhydrous, polymerization grade) is dissolved in 200 ml of toluene. To this solution is added 6.0 mM or 8.0 mM of cobaltous chloride (anhydrous) dispersed in toluene. The cobaltous chloride.caprolactam coordination complex forms immediately and goes into solution in the toluene upon gentle heating. Any

temperature between 0 and 50 C. may be used, but about 50 C. is preferred.

The solution turns blue immediately and becomes an intense, deep blue when the reaction mixture is heated to C. for 15 minutes. The reaction mixture can be heated to any temperature between about 50 and C. Cooling the toluene solution of cobaltous chloride.(- lactam) 8 to about 10 to 20 C., and preferably 5 C., is followed by reduction with 57 mM of triisobutyl aluminum. The blue solution changes to brown, the reduced compound remaining in solution. This solution is then used for hydrogenation of the elastomer. In"carrying out the reaction, the molar ratio of cobaltous chloride/lactam/triisobutyl aluminum is substantially 1:6:6 or 1:8:8. More generally, the molar ratio of the cobaltous lactam or other amide to the aluminum compound is substantially 1:6 or 1:8.

HYDROGENATION The hydrogenation reaction may be carried out in a stainless steel autoclave equipped with a pressure gauge and appropriate plumbing for introducing hydrogen into the reactor. The unsaturated elastomer is dissolved in an organic solvent. The temperature of the autoclave is adjusted to about 122 C. and then the catalyst is added to the solution with continuous stirring. The amount of catalyst used is between about 0.02 mM and 1.0 mM per gram of elastomer. The hydrogenation reaction proceeds immediately, and within 1 to 2 hours the hydrogenation is completed. The refractive index of the rubber may be used to measure the uptake of hydrogen. The polymer is isolated and characterized by NMR which shows the absence of olefinic peaks between 275 and 325 Hz.

The hydrogenation conditions can be varied depending upon the particular polymer to be hydrogenated. Normally hydrogenation reactions can be carried out at temperatures ranging from 25 to 500 C. However, the preferred conditions are 25 to 150 C. with pressures ranging from about 20 to 15000 psig., and the preferred range is 100 to 300 psig., and preferably from 25 to 1000 psig. For elastomers that contain terminal or internal oletinic units, for example, polybutadiene, polyisoprene, butadiene-isoprene copolymers, butadiene-styrene copolymer, butadiene-ethylene copolymers, isoprene-isobutylene copolymer; isopreneethylene copolymer, butadiene-isobutylene copolymer, butadiene-vinyl chloride copolymer, isoprene-vinyl chloride copolymer, butadiene-propylene copolymer and isoprenepropylene copolymer, etc., the preferred hydrogenation temperature ranges from 1 to C. at pressures of 25 to 500 psig. However, for rubbers that contain some aromatic groups, such as butadienestyrene, etc., the preferred hydrogenation conditions are temperatures between 0 and 120 C. and pressures of 500 to 15000 psig.

The length of the hydrogenation time is not too critical and may be from 1 minute to 20 hours, depending upon the process employed and the rubber used.

The catalyst system described herein can be used for selective hydrogenation of various unsaturated aliphatic and aromatic groups. It may be used for hydrogenation of terminal olefins in addition to internal olefins, such as 1,2-polybutadiene, etc.

The extent of the hydrogenation can be controlled by the amount of hydrogen introduced, and the rate at which the hydrogenation takes place is controlled by the temperature and the pressure.

EXAMPLE I prepared in 90 percent hexane. Any aliphatic solvent may be used. The solution is purged several times with hydrogen and with the temperature adjusted to 100C; 1.0 mM of cobaltous chloride.(caprolactam) complex reduced with 6 mM of triisobutyl aluminum is added and the reaction is subjected to hydrogen pressure of 200 psig. and agitated for 4 hours under constant 200 psig. hydrogen pressure. The reaction mixture is cooled to about room temperature and the polymer is coagulated by stirring it into isopropanol.

The polymer is completely saturated indicating complete hydrogenation of the polymer has been accomplished as shown by the characteristic absorption peaks at 100 Hz of aliphatic methylene groups obtained by NMR analysis. The spectrum was void of any olefinic groups at 275-325 Hz.

EXAMPLE II EXAMPLE Ill The procedure of Example I is followed, using 200 grams of butadiene-styrene (75/25) copolymer and 1.0 mM cobaltous chloride.(lactam) and 8.0 mM trialkyl aluminum. The NMR analysis showed complete hydrogenation.

EXAMPLE IV The procedure of Example III is followed, but using a hydrogenation temperature of 250 F. and pressure of 200 psig. Analysis by NMR shows 100 percent hydrogenation.

EXAMPLE v The procedure of Example IV is followed, but using a hydrogenation temperature of 300 F. and hydrogenation pressure of 200 psig. Analysis shows 60-70 percent hydrogenationby NMR.

I claim:

1. The process of hydrogenating an unsaturated elastomer which comprises hydrogenating the same in solution in an aliphatic solvent in the presence of 0.02 mM to 1.0 mM per gram of elastomer of a catalyst which is reduced cobaltous chloride.(lactam 8 catalyst. which lactam having the formula in which n=0 to 20 and which reducing agent is a trialkyl or triaryl aluminum or a dialkyl or diaryl aluminum hydride at a temperature of 250 to 500 C. and a pressure of 25 to 1000 psig.

2. The process of claim 1 in which the elastomer is from the class consisting of homopolymers of conjugated dienes containing 4 to 8 carbon atoms, copolymers of such conjugated dienes and copolymers of such conjugated dienes and vinyl monomers and the hydrogenation is effected with a reduced cobaltous chloride.(lactam 8 catalyst at 25 to 150 C. at a pressure of 100 to 300 psig.

3. The process of claim 1 in which the polymer is hydrogenated with cobaltous chloride.(caprolactam) or a catalyst at a temperature of 0 to 100 C. and a pressure of 25 to 500 psig. 

1. THE PROCESS OF HYDROGENATING AN UNSATURATED ELASTOMER WHICH COMPRISES HYDROGENATING THE SAME IN SOLUBLE IN AN ALIPHATIC SOLVENT IN THE PRESENCE OF 0.02 MM TO 1.0 MM PER GRAM OF ELASTOMER OF A CATALYST WHICH IS REDUCED COBALTOUS CHLORIDE. (LACTAM)6 OR 8 CATALYST WHICH LACTAM HAVING THE FORMULA
 2. The process of claim 1 in which the elastomer is from the class consisting of homopolymers of conjugated dienes containing 4 to 8 carbon atoms, copolymers of such conjugated dienes and copolymers of such conjugated dienes and vinyl monomers and the hydrogenation is effected with a reduced cobaltous chloride.(lactam)6 or 8 catalyst at 25* to 150* C. at a pressure of 100 to 300 psig.
 3. The process of claim 1 in which the polymer is hydrogenated with cobaltous chloride.(caprolactam)6 or 8 catalyst at a temperature of 0* to 100* C. and a pressure of 25 to 500 psig. 